The present invention relates to a hair trimmer for long hair, e.g. scalp hair or beard hair.
More particularly, the invention relates to a hair trimmer of this type which may be used to advantage in dryshavers and has a shear blade assembly of two contacting blades.
In this type of blade assembly one blade is usually stationary and the other slides on it and is reciprocated relative to it. Both blades have serrated cutting edges and hair enters into the serrations and is severed due to the reciprocation. A hair trimmer operating on this principle is known, e.g. from German Allowed Application DT-OS No. 2,019,978.
A problem with these trimmers is that the blades must tightly engage one another over their entire length and with the most uniform possible contact pressure--but that too much friction must be avoided. In the aforementioned prior-art trimmer the reciprocating blade engages the stationary blade--at its edge which is opposite the serrated cutting edge--only with one or a few projections, in order to avoid having to have a long continuous surface because that might lead to warping of the blade.
The two blades are urged into contact with one another by a biasing spring. To reduce the resulting friction the prior art proposes to interpose a glide bar between the spring and the reciprocating blade but--since friction is still high and may vary uncontrollably, due to fluctuations in manufacturing tolerances--it is also proposed to so construct the trimmer as a structural unit that it can be separately tested for proper functioning before being installed in a dryshaver.
This is technically a viable solution to the problem of excess friction because units exhibiting friction of a degree sufficient to interfere with proper operation can be discarded. However, the testing expenses and the costs of having to discard unsatisfactory units are high. From an economic viewpoint, therefore, a different solution is highly desirable.